Rotary expansible chamber devices – Shaft or trunnion lubrication or sealing by diverted working...
Patent
1995-10-06
1997-04-29
Freay, Charles G.
Rotary expansible chamber devices
Shaft or trunnion lubrication or sealing by diverted working...
418202, F01C 204, F01C 116
Patent
active
056242492
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a pumping process for operating a multi-phase screw pump with at least one feed screw surrounded by a housing, having at least one inlet and at least one outlet, with the intake medium being conveyed parallel to the screw shaft in a continuous low-pulsed stream and continuously discharged at the outlet.
The invention also relates to a multi-phase screw pump with at least one feed screw, surrounded by a housing, which has at least one inlet and at least one outlet, with the inlet communicating with a suction chamber located upstream from the feed screw and the outlet being connected with a pressure chamber located downstream from the feed screw.
The term "multi-phase" refers to a mixture of gas and liquid. In multi-phase transport, especially with high gas rates or dry running, the liquid is usually completely expelled. The feed elements then turn without a liquid to seal the gaps; the pump can no longer deliver the maximum pressure, which results in an interruption of feed. The heat of compression resulting from the compression of the gas phase can no longer be removed sufficiently. This results in overheating of the feed elements and their expansion with heat, which can result in destruction of the pump through contact with the housing.
In addition, with high gas rates or dry running, insufficient lubrication develops at the shaft seals, which can result in overheating at the shaft seals and hence to their destruction. When the residual liquid level on the inlet side is at the lower edge of the feed screws, the shaft seals are dry; the lubricant formed by the intake medium evaporates; the heat of friction is no longer removed which results in the destruction of the shaft seal. This problem is currently solved by permanent lubrication and cooling using an external seal oil assembly. These assemblies however are cost-intensive and prone to failure and therefore adversely affect the economy of such pumps.
The goal of the invention is to improve the pumping method described at the outset as well as the multi-phase screw shaft pump described at the outset in such fashion that neither extremely high gas content nor prolonged phases of dry running result in interruption of feed or in damage.
This goal is achieved according to the invention with respect to the pumping method by virtue of the fact that on the pressure side a partial liquid volume flow (liquid bypass) is separated and fed back into the intake area with metering, and is thus kept in circulation.
With regard to the pump, the stated goal is achieved according to the invention by virtue of the fact that a liquid bypass line is connected to a lower portion of the pressure chamber and communicates with the suction chamber.
According to the essential idea of the invention, therefore, assurance must be provided that sufficient liquid remains in the pump for safely performing its functions even at high gas rates or limited dry running, and is not expelled. This liquid remaining in the pump housing is intended to wet the shaft seals permanently and sufficiently, possibly in mist form.
The degree of separation required to achieve the stated goal and the volume of liquid to be kept in circulation can be determined on the basis of the housing and flow configurations. The metering of the liquid circulation can take place as a function of the pump differential pressure. However, it is also possible to connect a metering pump or a temperature-controlled valve in the liquid bypass line. It is advantageous in this regard if about 3% of the normal delivery flow is kept in circulation.
In order to facilitate separation of the liquid phase from the gas phase of the delivered medium in the pressure chamber, it is advantageous for the flowrate of the medium emerging from the feed screw on the discharge side to be reduced. This can be accomplished in the device by virtue of the fact that the pressure chamber has a cross section that increases as viewed in the direction of the through flow of the medium. In addition, flow guide means can be provide
REFERENCES:
patent: 4684335 (1987-08-01), Goodridge
patent: 4995797 (1991-02-01), Tsuboi
patent: 5348453 (1994-09-01), Baran et al.
"Screw Spindle Pumps for the Delivery of Multi-phase Mixtures", Pump Vacuum Compressors 1988 pp. 14-20.
Freay Charles G.
Joh. Heinrich Bornemann GmbH & Co. KG
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